Trump doubts NATO's loyalty to the US. Right?

"I like NATO. I'm just wondering, if we needed NATO, would they be there for us? I'm not certain if they would be," said president Donald Trump of the United States during an interview with journalists on Air Force 1 (https://defence24.pl/geopolitics/ Trump-o-grenland-nato-requires-us-a lot-more-niz-my-nato). Would the North Atlantic Alliance truly not be able to aid the US?